I have just come back from doing the ‘19 day Beach & bush’ which doesnt quite go as far as the Grand Aussie (only Sydney to Alice Springs) & I had such a fantastic time!!!
I am 22 & was also travelling alone, as were most of my the people in my group & we all got on so well, even with the people travelling as couples.
Our group ranged in age from about 20 -34 but age really want an issue at all - nobody cares how old you are when you are all there to have fun.
& the tour guides are fantastic too - we had Leigh & Lana up the East Coast & Nat & Nifty in the Northern Territory. They all hung out with us, & there was no pressure to do anything you didnt want to do, but the opportunities were there & they recommend making the most of your time while you are there.
I was really nervous before (& after) I booked my trip but now I am so glad I did it. I have made so many new friends & a week after being back home, I am still on a Topdeck high! My only regret is that I didnt do the Grand Aussie all the way to Darwin!
So I guess what I am trying to say is go for it! & I hope you have a fantastic time like my new friends & I did.